Transistor-transistor-logic (TTL) represents a widely used form of bipolar transistor circuit configurations. One of the latest and best known examples of this is the FAST.RTM. family of integrated circuit (IC) devices. The acronym stands for Fairchild Advanced Schottky TTL. National Semiconductor Corporation has published a databook covering this family of IC devices. It is titled "FAST.RTM. ADVANCED SCHOTTKY TTL LOGIC". The FAST.RTM. IC devices are fabricated using the well-known Isoplanar II technology which can produce IC transistors with very high, well-controlled switching speeds, extremely small parasitic capacitances and f.sub.T in excess of 5GHz. These transistors can employ Schottky diode clamps to avoid the turn-on delays normally associated with bipolar transistor saturation. The teaching in the above-mentioned databook is incorporated herein by reference.
In the following discussion the symbol .theta. (the Greek symbol for phi) is employed to designate a voltage equal to the base emitter voltage of a conducting junction transistor or the forward bias developed by a conducting PN junction diode. It is to be understood that a Schottky diode will develop a forward bias that is a fraction of that of a PN junction, or about .theta./2, when conducting. Also, a Schottky diode clamped junction transistor will produce a minimum on voltage drop of slightly over .theta./2 which is referred to as the saturation voltage.